1. Field of the Invention
The present invention relates to a snubber circuit for suppressing a surge voltage generated when a semiconductor switch used for a power converter turns OFF.
2. Related Art
A conventional snubber circuit provided with a capacitor for detecting a voltage between both ends of a semiconductor switch such as IGBT is known. This kind of capacitor is precharged with a power supply voltage and when a voltage higher than the supply voltage is applied to a device turned OFF due to energy stored in a parasitic inductance which exists in a main circuit, the capacitor absorbs the energy and suppresses a surge voltage. This operation is repeated every time the semiconductor device performs switching.
In this kind of conventional snubber circuit voltage detection lines of the capacitor are cross-connected, which results in a problem that the snubber circuit cannot be provided corresponding to each of a plurality of serially-connected semiconductor switches. Furthermore, the capacitor in the snubber circuit must have a high breakdown voltage structure when the supply voltage is a high voltage, which increases the cost and size.
In order to solve these problems, a circuit is disclosed (see Japanese Patent Laid-Open No. 2000-12780, Japanese Patent Laid-Open No. 2000-92817) which makes it possible to reduce the size and protect a plurality of serially-connected semiconductor switches from overvoltages.
However, such a circuit uses a high breakdown voltage and expensive device such as a zener diode or IGBT for voltage detection, which increases the cost of the snubber circuit.